Tree Data Structures &Binary Search Tree 1

Trees Data Structures Tree  Nodes  Each node can have 0 or more children  A node can have at most one parent Binary tree  Tree with 0–2 children per node TreeBinary Tree 2

Trees Terminology  Root  no parent  Leaf  no child  Interior  non-leaf  Height  distance from root to leaf Root node Leaf nodes Interior nodes Height 3

Binary Search Trees Key property  Value at node Smaller values in left subtree Larger values in right subtree  Example X > Y X < Z Y X Z 4

Binary Tree Implementation Class Node { int data; // Could be int, a class, etc Node *left, *right; // null if empty void insert ( int data ) { … } void delete ( int data ) { … } Node *find ( int data ) { … } … } 5

Binary Search Trees Examples Binary search trees Not a binary search tree

Example Binary Searches Find ( root, 2 ) > 2, left 5 > 2, left 2 = 2, found 5 > 2, left 2 = 2, found root 7

Example Binary Searches Find (root, 25 ) < 25, right 30 > 25, left 25 = 25, found 5 < 25, right 45 > 25, left 30 > 25, left 10 < 25, right 25 = 25, found 8

Iterative Search of Binary Tree Node *Find( Node *n, int key) { while (n != NULL) { if (n->data == key) // Found it return n; if (n->data > key) // In left subtree n = n->left; else // In right subtree n = n->right; } return null; } Node * n = Find( root, 5); 9

Recursive Search of Binary Tree Node *Find( Node *n, int key) { if (n == NULL) // Not found return( n ); else if (n->data == key) // Found it return( n ); else if (n->data > key) // In left subtree return Find( n->left, key ); else // In right subtree return Find( n->right, key ); } Node * n = Find( root, 5); 10

Types of Binary Trees Degenerate – only one child Complete – always two children Balanced – “mostly” two children  more formal definitions exist, above are intuitive ideas Degenerate binary tree Balanced binary tree Complete binary tree 11

Binary Trees Properties Degenerate  Height = O(n) for n nodes  Similar to linked list Balanced  Height = O( log(n) ) for n nodes  Useful for searches Degenerate binary tree Balanced binary tree 12

Binary Search Properties Time of search  Proportional to height of tree  Balanced binary tree O( log(n) ) time  Degenerate tree O( n ) time Like searching linked list / unsorted array 13

Binary Search Tree Construction How to build & maintain binary trees?  Insertion  Deletion Maintain key property (invariant)  Smaller values in left subtree  Larger values in right subtree 14

Binary Search Tree – Insertion Algorithm 1. Perform search for value X 2. Search will end at node Y (if X not in tree) 3. If X < Y, insert new leaf X as new left subtree for Y 4. If X > Y, insert new leaf X as new right subtree for Y Observations  O( log(n) ) operation for balanced tree  Insertions may unbalance tree 15

Example Insertion Insert ( 20 ) < 20, right 30 > 20, left 25 > 20, left Insert 20 on left 20 16

Binary Search Tree – Deletion Algorithm 1. Perform search for value X 2. If X is a leaf, delete X 3. Else // must delete internal node a) Replace with largest value Y on left subtree OR smallest value Z on right subtree b) Delete replacement value (Y or Z) from subtree Observation  O( log(n) ) operation for balanced tree  Deletions may unbalance tree 17

Example Deletion (Leaf) Delete ( 25 ) < 25, right 30 > 25, left 25 = 25, delete

Example Deletion (Internal Node) Delete ( 10 ) Replacing 10 with largest value in left subtree Replacing 5 with largest value in left subtree Deleting leaf 19

Example Deletion (Internal Node) Delete ( 10 ) Replacing 10 with smallest value in right subtree Deleting leafResulting tree 20

Balanced Search Trees Kinds of balanced binary search trees  height balanced vs. weight balanced  “Tree rotations” used to maintain balance on insert/delete Non-binary search trees  2/3 trees each internal node has 2 or 3 children all leaves at same depth (height balanced)  B-trees Generalization of 2/3 trees Each internal node has between k/2 and k children  Each node has an array of pointers to children Widely used in databases 21

Other (Non-Search) Trees Parse trees  Convert from textual representation to tree representation  Textual program to tree Used extensively in compilers  Tree representation of data E.g. HTML data can be represented as a tree  called DOM (Document Object Model) tree XML  Like HTML, but used to represent data  Tree structured 22

Parse Trees Expressions, programs, etc can be represented by tree structures  E.g. Arithmetic Expression Tree  A-(C/5 * 2) + (D*5 % 4) + - % A * * 4 / 2 D 5 C 5 23

XML Data Representation  E.g. sample1.o sample1.cpp sample1.h g++ -c sample1.cpp  Tree representation dependency objectdepends sample1.osample1.cpp depends sample1.h rule g++ -c … 24

Graph Data Structures E.g: Airline networks, road networks, electrical circuits Nodes and Edges E.g. representation: class Node Stores name stores pointers to all adjacent nodes  i,e. edge == pointer  To store multiple pointers: use array or linked list Ahm’bad Delhi Mumbai Calcutta Chennai Madurai 25

End of Chapter 26